The indoor environment is often contaminated with a variety of noxious and toxic gases including carbon monoxide, methane, sulfur dioxide, hydrogen sulfide, NO.sub.x, and a broad variety of organic vapors. Some of these are widely prevalent in the environment, particularly in urban areas, and others tend to be pronounced in homes, offices, or other confined spaces due to activities within those spaces.
Noxious or toxic materials may be produced from tobacco smoking, cooking, open fireplaces, faulty appliances, or a variety of other normal activities. Some of these are merely unpleasant because of odors; others, such as products of smoking or cooking, may accumulate and soil surfaces; while others, such as carbon monoxide, may be dangerous. It has been found, for example, that a high proportion of homes have unsuspected carbon monoxide concentrations which contribute to vague disorders such as lassitude and headaches at concentrations far below levels that produce overt symptoms of toxicity.
Unwanted particles are also commonly found in the environment. Tobacco smoking produces particles as well as gases. Organic aerosols, dust particles, pollen and minute organisms may also float in the air. In some dusty areas such particles can be hazardous due to the chemical nature of the particles, or just due to the fine particle size. Environmental standards have been promulgated for particles smaller than ten micrometers since these penetrate much deeper into the lungs than coarser particles.
Clearly, it is desirable to reduce the concentrations of such noxious and toxic materials in the indoor environment.
A variety of devices have been marketed over the years to assist in this regard. Negative ion generators are regarded by some as effective. However, they are effective largely for particles, and do not provide broad spectrum removal of many gases. Room air fresheners do very little but mask the problem with more acceptable vapors. Activated charcoal filters may be used, but they are fairly costly and eventually lose their activity as the activated sites on the charcoal are used up. It is also difficult to assess whether such filters remain effective, and they may be prematurely discarded or kept in service long after their useful life.
It is, therefore, desirable to provide an air purifier for use indoors for reducing the concentrations of particulates, and noxious and toxic gases in the air. It is desirable that this apparatus operate effectively for long periods without being exhausted or require costly replacements. It is desirable that it be effective with respect to a broad variety of noxious and toxic materials. It is desirable that it be simple and require low maintenance. It is also highly desirable that it be attractive since it becomes a permanent fixture in the indoor environment.